-----Yogurt is a dairy product produced by bacterial fermentation of milk. Fermentation of the milk sugar or what we call lactose produces lactic acid, which acts on milk protein to give yogurt its texture and its characteristic tang. It is nutritionally rich in protein, calcium, riboflavin, vitamin B6, and vitamin B12.
-----There is evidence of cultured milk products being produced as food for at least 4,500 years. The earliest yogurts were probably spontaneously fermented by wild bacteria living on the goat skin bags carried by nomadic people. Today, many different countries claim yogurt as their own invention, yet there is no clear evidence as to where it was discovered, and it may have been independently discovered several times.
-----Yogurt was first introduced to the United States by Armenian immigrants Sarkis and Rose Colombosian, who started "Colombo and Sons Creamery" in Andover, Massachusetts in 1929. Colombo Yogurt was originally delivered around New England in a horse-drawn wagon inscribed with the Armenian word "madzoon" which was later changed to "yogurt", the Turkish name of the product, as Turkish was the lingua franca between immigrants of the various Near Eastern ethnicities who were the main consumers at that time. Yogurt's popularity in the United States was enhanced in the 1950s and 60's when it was presented as a health food. By the late 20th century yoghurt had become a common American food item and Colombo Yoghurt was sold to General Mills in 1993.
-----Yogurt is made by introducing specific bacteria strains into milk, which is subsequently fermented under controlled temperatures and environmental conditions or inside a bioreactor, especially in industrial production. The bacteria ingest natural milk sugars and release lactic acid as a waste product. The increased acidity causes milk proteins to tangle into a solid mass (curd) in a process called denaturation. The increased acidity (pH = 4–5) also prevents the proliferation of potentially pathogenic bacteria. In Australia and Bulgaria, to be named yoghurt, the product must be made with the bacterial species Streptococcus salivarius subsp. thermophilus and Lactobacillus delbrueckii subsp. bulgaricus. Often these two are co-cultured with other lactic acid bacteria for taste or health effects. These include L. acidophilus, L. casei and Bifidobacterium species. In most countries, a product may be called yoghurt only if live bacteria are present in the final product. In Australia, non-pasteurised yoghurt can be marketed as "live" or containing "live active culture". A small amount of live yoghurt can be used to inoculate a new batch of yoghurt, as the bacteria reproduce and multiply during fermentation. Pasteurised products, which have no living bacteria, are called fermented milk (drink).
